Heat-treating aluminum silicon alloy

ABSTRACT

A method for increasing the amount of free aluminum in an aluminum-silicon-alloy-containing iron and titanium as impurities which comprises heating the alloy to a temperature of from about 400* C. to about 1,200* C. for at least 2 hours sufficient to decrease the amount of aluminum chemically bound in the form of intermetallic compounds.

United States Patent [72] Inventors ClarenceLl-lildreth Baton Rouge; Sebastian M. Laurent, Greenwell Springs, both oiLa.

[21] AppLNo. 43,229

[22] Filed June3, 1970 [45] Patented Dec.7, 1971 [73] Assignee Ethyl Corporation New York, N .Y.

[54] HEAT-TREATING ALUMINUM SILICON ALLOY [56] References Cited UNITED STATES PATENTS 3,503,737 3/1970 Layne et al. 75/68 3,1 16,997 l/l964 Kohimeyer et a1 75/68 Primary ExaminerRichard 0. Dean Attorneys-Donald L. Johnson, John F. Sieberth, David L.

Ray and Arthur G. Connolly HEAT-TREATING ALUMINUM SILICON ALLOY BACKGROUND OF THE INVENTION This invention relates to a process for increasing the amount of aluminum recovered from aluminum-containing ores. More specifically, this invention relates to the recovery of aluminum from aluminum-containing compounds found in aluminum-silicon alloys.

Methods for the production of aluminum-silicon alloys are well known in the prior art. Typical is the method disclosed in U.S. Pat. No. 3,1 l6,997. Another well-known process is the electric arc furnace process. Most processes for forming aluminum-silicon alloys include the steps of heating the ore in a furnace, tapping the furnace, pouring out the molten alloy, and cooling the alloy.

. Aluminum-silicon alloys generally contain significant amountsof iron and titanium impurities. The iron and titanium impurities unite with the aluminum during the cooling of the molten alloy to form various intermetallic compounds. Such intennetallic compounds have very high energies of formation which makes the liberation of aluminum contained in these compounds extremely difficult.

The intermetallic compounds may be composed of two, three or four elements. Typical of such intermetallic compounds are TiAl FeAl FeSi Al Al Ti,Si,,, and the like. Various techniques are known in the art by which these intermetallics can be separated from the aluminum-silicon alloy and removed. However, no simple method is known for extracting usable elementary aluminum from these intermetallic compounds easily and economically.

ln aluminum-silicon alloys that contain iron but no titanium, the iron will unite with aluminum to form FeAl However, if small amounts of titanium are also present FeSi Ah is formed. The titanium catalyzes the formation of FeSi,Al but the titanium does not become part of the compound itself. The titanium usually united with aluminum to form TiAl Both FeSi Al and TiAl are highly undesirable compounds because the aluminum contained in these compounds is not commercially usable. The amount of aluminum contained in these compounds is quite significant. Approximately two pounds of aluminum are combined with every pound of iron present in FeSi Al, and approximately 1.7 pounds of aluminum are combined with every pound of titanium in TiAl;,. Since conventional technology can only produce aluminumsilicon alloys with aluminum contents no higher than 60-70 percent, the two pounds of aluminum per pound of iron tied up in FeSi AI or the 1.7 pounds tied up in TiAl. represents a significant proportion of the aluminum present.

THE INVENTION The object of this invention is to increase the amount ofaluminum recoverable from aluminum-silicon alloys.

Another object of the invention is to free aluminum from aluminum-containing intermetallic compounds.

A further object of the present invention is to convert FeSi Al, and TiAl; to Fe Ti and Al Ti Si,,.

The foregoing objects are realized in a method for increasing the amount of free aluminum in an aluminum-silicon alloy containing iron and titanium as impurities which comprises heating the alloy to a temperature in the range of about 400 C. to about l,200 C. for at least about 2 hours sufficient to decrease the amount of aluminum chemically bound in the form of intermetallic compounds.

The aluminum-silicon alloys which are heat treated in accordance with the present invention are prepared by any of the conventional processes well known in the art. Typical of these processes is US. Pat. No. 3,l 5,997, which is hereby incorporated by reference. The alloys may also be prepared by mechanically mixing aluminum, silicon, iron and titanium together, and then heating the mixture to the molten state.

The aluminum-silicon-iron-titanium alloys treated in accordance with the present invention are heated in any conventional heating apparatus or oven to a temperature of from about 400 C. to about l,200 C. A more preferred temperature range is from about 500 C. to 800 C. The molten or solid aluminum-silicon-iron-titanium alloy should be heated for at least about 2 hours. A preferred minimum heating time is at least 6 hours. A more preferred minimum heating time is at least 18 hours.

The alloys which may be treated in accordance with the present invention must contain aluminum, silicon, iron and titanium. The amount of aluminum in the alloy may range from about 30 weight percent to about 75 weight percent. A preferred range is from about 50 weight percent to about 65 weight percent. 7

The amount of silicon in the alloy may range from about 10 weight percent to about 50 weight percent. A preferred range is from about 25 weight percent to about 40 weight percent.

The amount of iron in the alloy may range from about 0.5 weight percent to about 10 weight percent. A more preferred range is from about 2 weight percent to about 5 weight percent.

The amount of titanium in the alloy may range from about 0.5 weight percent to about l0 weight percent. A preferred range is from about 2 weight percent to about 5 weight percent.

Various minor amounts of other impurity elements may be present within the alloys, but these elements have no effect on the process of the present invention. These impurities may include manganese, chromium, nickel, vanadium, and the like.

The atmosphere surrounding the alloy during the heat treatment is of no significance. The atmosphere may be oxidizing, reducing, or neutral. lt is also immaterial whether the alloy be brought into the furnace for heat treating at a temperature below that at which the furnace is operating or whether the alloy be brought into the furnace at a higher temperature than that of the furnace.

The intermetallic compounds which are eliminated in accordance with the present invention include FeSi Al, and TiAl These compounds are formed in all known processes for producing aluminum-silicon-iron-titanium alloys. These compounds generally exist in an amount proportional to the amount of iron or titanium in the alloy. It is believed that heat treatment in accordance with the present invention causes Fe Ti to be preferentially formed, thus freeing iron from FeSi Al and leaving the other elements of the compound available to form a new compound, Al Ti Si The compound Fe Ti is formed until all of the iron in the alloy is used up. The excess Ti remaining determines the amount of Al Ti Si which is formed.

The heat treatment process of the present invention raises the temperature of the alloy, and therefore the individual elements (iron, titanium, aluminum, and silicon) can move more freely throughthe alloy. The greater mobility of the various elements in the alloy makes the conversion of the undesirable intermetallics much more rapid. At room temperature the mobility is so slight that no such change occurs even over long periods of time.

The examples displayed in the table were prepared as follows: The number of grams of each particular element indicated in the table were placed in a graphite crucible. The graphite crucible was placed in an insulated ceramic crucible, heated in an induction furnace to a temperature of about l,900 C., and the contents of the crucible were stirred with a graphite rod. The crucible was removed from the induction furnace and allowed to cool to room temperature. The alloy was placed in a small ceramic crucible and surrounded by either lamp black or aluminum oxide, and the crucible was placed in a muffle furnace at room temperature. The muffle furnace was then heated to the desired heat-treating temperature and left there for the number of hours indicated in the table. The sample was removed from the furnace and allowed to cool to room temperature. The sample was placed on a lathe and the outer skin removed to eliminate oxidation products. The remaining ingot was comminuted and analyzed by X-ray diffraction techniques for determination of the amount of each intermetallic as a percentage of the total alloy.

TABLE OF EXAMPLES Composition, parts Heat treatment by Weight (grams) Percentage ai Si Fe T1 (hrs.) C.) FeSizAh TiAh 34 4 No treatment 2 34 4 5 18 500 5 0 34 4 5 18 750 1 0 31. 3 10.7 2. 3 No treatment 23 0 31. 3 10. 7 2. 3 18 750 6 3 35 2. 5 3. 0 No treatment 4 1 35 2. 5 3.0 18 500 2 0 35 2. 5 3.0 9 500 1 1 35 2. 5 3.0 18 750 1 0 35 2. 5 0. 5 No treatment 4 1 35 2. 5 0. 5 1 500 3 Trace 35 1. 0 0. 5 No treatment 1 0 35 1. 0 0. 5 18 500 Trace 0 EXAMPLE 14 Example 3 is repeated with the exception that the heat treatment temperature is l,200 C. The same percentages of Fesi Al and TiAl are achieved.

EXAMPLE 15 The alloy of example 6 is heat treated at a temperature of l,200 C. for 2 hours. The percentage of FeSi Al is slightly reduced, but the percentage of TiAl is not noticeably changed.

EXAMPLE 16 p 4 showed drastic reduction of the amount of FeSi,Al and TiAl in the alloy.

What is claimed is:

l. A method for increasing the amount of free aluminum in an aluminum-silicon alloy containing iron and titanium which comprises heating said alloy to a temperature of from about 400 C. to about l,200 C. for at least about 2 hours.

2. The method of claim 1 wherein said alloy is heated for at least about 6 hours.

3. The method of claim I wherein said alloy contains from about 30 weight percent to about 75 weight percent of aluminum, from about 10 weight percent to about 50 weight percent of silicon, from about 0.5 weight percent to about 10 weight percent iron, and about 0.5 weight percent to about 10 weight percent titanium.

4. The method of claim 1 wherein said alloy contains impurities.

5. The method of claim 1 wherein said alloy is heated from about 500 C. to about 800 C.

6. A method for decreasing the amount of FeSi AL and TiAl in aluminum-silicon alloys containing iron and titanium which comprises heating said alloy to a temperature of from about 400 C. to about 1,200 C. for at least about 2 hours, and cooled to room temperature.

7. The method of claim 6 wherein said alloy contains from about 30 weight percent to about 75 weight percent of aluminum, from about 10 weight percent to about 50 weight percent of silicon, from about 0.5 weight percent to about 10 weight percent iron, and about 0.5 weight percent to about 10 weight percent titanium.

8. The method of claim 6 wherein said alloy is heated from about 500 C. to about 800 C.

9. The method of claim 6 wherein said alloy is heated for at least about 6 hours.

22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION Patent No. 625. 778 Dated December 7, 1971 Inventor) Clarence L. Hildreth and Sebastian M. Laurent It is certified that error appears in the above-identified patent and that said Letgers Patent are hereby corrected as shown below:

Column 1, line #9, reads "TiALQ', should read 'I'iAl should read in Column 5, line 5 reads is Signed and sealed this 25in day of April 1972.

(SEAL) Attest:

EDWARD M.FLETCH1-JR,JR. ROBERT GOTTSCHALK Attestinp; Officer Commissioner of Patents 

2. The method of claim 1 wherein said alloy is heated for at least about 6 hours.
 3. The method of claim 1 wherein said alloy contains from about 30 weight percent to about 75 weight percent of aluminum, from about 10 weight percent to about 50 weight percent of silicon, from about 0.5 weight percent to about 10 weight percent iron, and about 0.5 weight percent to about 10 weight percent titanium.
 4. The method of claim 1 wherein said alloy contains impurities.
 5. The method of claim 1 wherein said alloy is heated from about 500* C. to about 800* C.
 6. A method for decreasing the amount of FeSi2Al4 and TiAl3 in aluminum-silicon alloys containing iron and titanium which comprises heating said alloy to a temperature of from about 400* C. to about 1,200* C. for at least about 2 hours, and cooled to room temperature.
 7. The method of claim 6 wherein said alloy contains from about 30 weight percent to about 75 weight percent of aluminum, from about 10 weight percent to about 50 weight percent of silicon, frOm about 0.5 weight percent to about 10 weight percent iron, and about 0.5 weight percent to about 10 weight percent titanium.
 8. The method of claim 6 wherein said alloy is heated from about 500* C. to about 800* C.
 9. The method of claim 6 wherein said alloy is heated for at least about 6 hours. 